1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine having an exhaust-driven turbocharger.
2. Description of the Background Art
Control of the internal combustion engine (engine control) is performed by adjusting for example such an engine control variable as fuel injection timing based on such engine parameters as accelerator pedal position and engine speed. As a target control value of the engine control variable used for the engine control, basically a value appropriate for a steady operating state of the internal combustion engine is set.
One type of the internal combustion engine is an internal combustion engine having an exhaust-driven turbocharger operated using the force of exhaust flow. A change in quantity of intake air of the internal combustion engine involves a predetermined delay in response for the following reason. When the operating state of the internal combustion engine is changed, the quantity of exhaust is changed first. Then, the change in quantity of exhaust causes a change in state of supercharging by the turbocharger and accordingly causes a change in intake air quantity. Therefore, when the operating state of the internal combustion engine in a steady operating state is changed, the internal combustion engine enters a transient operating state in which there is a difference between an intake air quantity appropriate for the above-described engine parameters and an actual intake air quantity. Then, after a predetermined period of time, the internal combustion engine enters the steady operating state again.
While the internal combustion engine is in such a transient operating state, even if the engine control variable is simply adjusted based on the engine parameters, the adjusted engine control variable is not appropriate for the actual intake air quantity, resulting in various disadvantages such as deterioration in emission properties and an increase in combustion noise.
Thus, it has been proposed to adjust the engine control variable while making corrections according to a difference between a target intake air quantity and an actual intake air quantity for engine control, as done by the apparatus disclosed in Japanese Patent Laying-Open No. 2002-021613. While the internal combustion engine is in the transient operating state, this apparatus uses a correction factor which is determined according to the degree of the above-described difference in intake air quantity to correct the engine control variable, and accordingly prevent the aforementioned disadvantages from being caused.
It should be noted that, even in the case where the above-described difference in intake air quantity is the same, the correction factor determined according to the difference is not always the same. The correction factor varies depending on the engine operating conditions including for example fuel injection quantity and intake air quantity at the time. Therefore, even if the engine control variable is simply adjusted in the manner according to the deviation, namely the degree of the difference in intake air quantity as described above, the aforementioned disadvantages cannot appropriately be avoided. In this respect, the conventional apparatus still requires improvements.